Taking https://bugzilla.redhat.com/show_bug.cgi?id=1298935 upstream:

Since gdm switches TTY when logging in a user, the "gnome-shell --mode=gdm" process keeps consuming a lot of CPU (about 40% on my system) after a user has been logged in when using a binary NVIDIA driver. It may return to the normal value of below 1% of a CPU core some minutes or hours later on its own or keep burning the CPU indefinitely.

The issue doesn't exist with nouveau or with Intel graphics. I don't have any AMD graphics hardware to test.

STR:

1. Make sure the binary NVIDIA driver is installed and active.

2. Start a new user session from gdm.

3. Check the output of "top -u gdm".

Actual Results:

The "gnome-shell --mode=gdm" background process constantly consumes a substantial amount of CPU resources.

Expected Results:

The CPU load from the aforementioned process drops immediately close to zero once a user session has been initiated.

rpm -q gnome-shell gdm
gnome-shell-3.18.3-1.fc23.x86_64
gdm-3.18.2-1.fc23.x86_64

NVIDIA binary driver version 352.79 (tested with 340.96 and 361.18 as well with the same results)

Switching TTY to gdm and back works around the issue for the current user session.